Fuse



March 31, 1942.

Top END FIGURE 3 Filed May 1,1939

A. J. IBOWIE 2,278,058

. FUSE TOP END /4 A A 20 (55673-3) Hal/2 54- A3 I 4 I I F /7 g I I I Y I I /5\ Heuez I v Wmmmmvroa 2 Sheets-Sheet 1 Patented Mar. 31, 1942 outrun STATESLHPATENT OFFICE 21 Claims.

The object of this invention is to increase the reliability of operation of fuses under both light and heavy loads. To take care of the light load condition I preferably use the materials such as gun powder as an example which would ignite when the fuse blows and will give sufficient pressure to effect the necessary fuse operation. While the use of gun powder is not novel my construction has improved features.

In its preferable form I utilize a fuse tube with ferrules on the ends, both ends being hermetically closed to the atmosphere in order to exclude both moisture and dirt which have deteriorating effects on operation. One of the essential requirements of a fuse is to take care of the high pressure generated when the fuse blows. It is generally preferred to have the fuse tube blow out at one predetermined end. However to care for very high pressures the other end of the fuse tube is also made so that it will open and thus act as a safety valve with a time delay element which insures proper operation of the fuse.

It is a well established principle in fuses that quenching insulating material, preferably powdered, is of benefit in extinguishing the arc. One of the difficulties experienced in fuses filled with insulating powder is that the pressure within the tube which is generated when the fuse blows must be transmitted through a column of powdered filled to the seal for the fuse tube in order to expel the sealing member. This column of filler when of any length bridges and does not allow the ready transmission of pressure to the seal, thus resulting in premature rupture of the fuse tube.

It is one object of my invention to obtain means of definitely and instantly transmitting pressure generated by the arc to the sealing member largely independent of direct pressure on the filling material within the tube. If the seal is of metal and contacts with the ferrule an arc is established between the ferrule and the seal when the seal blows out. As the seal moves out this are tends to take the shorter path between the expelled fuse wire and the end ferrule. When the insulating powder filling the fuse is expelled this is driven through the arc and tends to extinguish it. As the distance from the fuse wire to the ferrule is relatively small the arcing length may be increased by surrounding the fuse with insulating material which allows a greater rupturing capacity. Further a small insulating guide on the end of the fuse serves to direct the flow of the filler material when the fuse blows and thus to aid in extinguishing the arc.

Fig. 1 shows the longitudinal cross-section of one type of fuse, the end sections being circular.

Fig. 2 shows cross-section on the line H.

Fig. 3 shows the longitudinal section of another type of fuse.

Fig. 4 is a section along the line bb.

Fig. 5 is a longitudinal cross-section of lower end of fuse tube the upper end of which is similar to that shown in Fig. 1.

Fig. 6 is a cross-section thereof on the line 0-0.

Fig. 7 is an alternate construction in longitudinal section similar to the fuse shown in Fig. 3.

I is a fuse tube with top ferrule 2. 3 is a top cap. 4 is a light cap closing the top of 3, the function of which is to keep moisture from entering the top of the fuse. 5 is a metal retaining washer for the inner fuse tube 5 which latter is preferably constructed of fibre. Retaining washer 5 normally retains the top fuse disc I. 8 is a conductor connected at the top to fuse element 9. I0 is a high resistance strain element to take care of the mechanical tension of the fuse. II is a container for the fuse element which is filled with gun powder [2. l3l3 are end sealing plugs in the tube II. M is a conductor, preferably flexible, through which the current is taken to the cap l5 which contacts with bottom ferrule IE on which mounts insulating tube l1 having a stop pin l8. I9 is an insulating tube fitting with a sliding fit in tube 6 and provided with top cap 20. 2| is a granular filler of arc extinguishing material in the lower part of the tube.

The corresponding parts apply to Fig. 3 except that in addition 22 is an upper cap which blows out at a materially higher pressure than is required for the lower contact cap I5. This cap makes a frictional contact with ferrule 2. The action of the fuse is as follows:

When the fuse melts the gun powder is ignited, exerting pressure on tube I9, which immediately forces out the cap [5 which starts an arc with ferrule Hi. This is followed by the flow of the insulating material 2| between cap I5 and ferrule l6 as it moves out. The tube l9 prevents the re-establishment of the are between the conductor l4 and ferrule l6, and the guiding inner surface of insulating tube I! directs the flow of expelled powder filler 2| directly into the arc. The function of the stop pin I 8 is primarily a limit stop to prevent the forcible ejection of tube is. With tube l9 sliding in tube 6 for a material distance, the action is similar to that of a projectile in the barrel of a gun, and desired velocity is in turn transmitted to the tube [9.

Experience has shown that with the filler 2| not entirely filling the space between tubes 1 and I9 there is provided an air space which allows the handling of very high pressure without rupture of the tubes when the fuse blows, since otherwise the leakage between tubes l9 and 6 may be sufficiently high to allow the pressure to burst the outer tube. This makes an important safety factor. The fuse top disc "I will be driven out of retaining washer 5 by excessive pressure but this requires an appreciable element of time which is desirable to allow the bottom parts of the fuse to function properly. This provides an' important safety factor in the time necessary to draw the disc 1 into a cup shape through the retaining washer 5. When this disc is expelled it strikes cap 4 which is a light press fit and drives it off. It is essential to have the pressure of the blown fuse transmitted rapidly to cap 15. The tube l9 acts as a direct strut giving the desired effect. The button 2i) may or may not be supplied. If it is omitted the pressure of the blowing fuse will be transmitted through the tube l9 as well, but it will in any event eject cap l5. This button 20, at the end of the in sulating tube I9, under less violent fuse action may serve as a plug, thus increasing the shock pressure transmitted directly through the wall of the insulating tube is. But under any violent fuse action where instantaneous pressures may be dangerous the button, being of yieldable material, yields and the air column within the tube becomes effective as a cushion. However, the shock pressure in the fuse chamber is under all conditions directly transmitted to the sealing member through the annular wall of the thrust tube resulting in more rapid and positive expulsion of the cap 15 than if, as in the present fuses on the market, the pressure is transmitted through a body of air or of granular or powdered arc extinguishing material.

In the design shown in Fig. 3 cap 22 is made to blow out at a materially higher pressure than cap 15. In this case the filler 2| extends throughout the tube. The pressure caused by the blowing of the fuse is correspondingly transmitted to the bottom cap 15. If desired the tube 19 may be sufficiently light to transmit a moderate amount of pressure to the cap 15 and then to collapse under extreme pressure. This collapse under these conditions is a safety feature as it allows the flow of filling material inward and prevents the wedging of filling material under excessive internal pressure. It will thus be seen that gun powder though it may be omitted is an aid to the interrupting of very light loads, in fact the charge is made extremely light. The problem of all heavy loads is one of disposing of very high bursting pressure. Under these conditions the gun powder would not be of any benefit but inasmuch as its amount is small its detriment is practically negligible.

The fuse shown in Fig. '7 is similar to that shown in Fig. 3 except that the top end of the fuse is provided with a conductor 8 surrounded by an insulating tube ISA, the arrangement being such that the insulating tubes will act on both ends and will convey the pressure generated when the fuse blows to both ends caps. In order to make a differential action in favor of one end blowing out first it is preferable to stop the upper tube IQA short of the cap 22. As a result when the fuse blows cap IE will first be blown out but if the pressure is sufficiently great to endanger the bursting of the tube both caps l5 and 22 will be blown out.

Experience has shown that the air space between conductor Hi and the surrounding tube I9 which is preferably made of horn fibre, is of great importance in taking care of the high initial pressure. In other words the intervening air space serves as an air reservoir which cushions the instantaneous effect of the pressure generated when the fuse blows. In general these tubes I!) have the ends lightly sealed to exclude entirely the filling material, but when pressure is generated when the fuse blows these seals will instantly yield and allow the internal air space to cushion the pressure occasioned by the blowing of the fuse, and to transmit internal pressure directly to the sealing cap It.

In the fuse shown in Fig. 5 the conductor M is securely connected to ferrule IE and the tube I9 is closed at its lower end by a plug through which the conductor I i freely passes. 24 is a restriction placed within the tube which fits with a sliding fit over tube ill which is provided with a rounded lower edge. The plan of this construction is to provide a fuse with a very rapid break and to provide a restriction for the flow of insulating filling until it is desired to have it expelled.

The action is as follows: When the fuse blows the tube i9 is driven outward expelling the cap it. As the conductor ii is anchored to ferrule it is also drawn through the tube it through the action of the lower edge of the tube on conductor I l. The speed of motion of the upper end of It hence is double that of tube l9 while being ejected. The powdered filler is largely held in place until tube i9 is driven out of the bottom ferrule of the fuse, at which time the powdered filler is freely discharged, but in the intervening time as soon as tube it has reached a point below the filling material this material will also be driven into the are within the tube l9 thus giving a double means of extinguishing the are.

In all the forms of the invention shown it will be seen that the pressures generated by the fusing of the fusable element are transmitted directly by shock action through the thrust member to the sealing cap thus giving it a hammer lilre blow and insuring unsealing of the fuse tube. As this insulating tube is expelled it passes through the granular arc extinguishing material thus agitating it and permitting it to expand into the space formerly occupied by the insulating tube thus relieving the tendency for the arc extinguishing material to pack and bridge and insuring its expulsion. It will also be noted that the insulating tube extends through the compartment containing the fusible element 9 sufficiently far that the sealing cap i5 is expelled prior to the admission of pressure to the face of the arc extinguishing material, the insulating tube serving as a valve. This likewise prevents packing of the arc extinguishing material by the explosion pressure as the pressure does not come upon this material until it may be freely expelled through the fuse tube.

Having thus described my invention I claim and desire to secure by Letters Patent:

1. A fuse including a fuse tube, terminal connections therefor, a conductor connecting said terminal connections, at least a portion thereof being readily fusible. and a sealing member electrically conecting said conductor to one of said terminal connections and adapted normally to close one end of said fuse tube, a thrust member within said fuse tube extending from the readily fusible portion of said conductor toward said sealing member and adapted upon the fusing of said fusible portion to transmit the force caused by the expanding gases resulting from the blowing of the fuse directly to the sealing member, whereby the tube is rapidly unsealed, and a body of arc extinguishing material retained by said sealing member and adapted to be injected into the are formed upon the expulsion of said sealing member.

2. A fuse including a fuse tube, terminal connections therefor, a conductor connecting to said terminal connections, at least a portion thereof being readily fusible, a sealing member adapted normally to close one end of said fuse tube and electrically connect ng said conductor of one of said terminal members, an insulating tubular thrust member within said tube containing part of said terminal connections and extending to ward said sealing member, said thrust member being adapted to be expelled by the gases formed by the blowing of the fusible member, and thereby to create an insulating path when said sealing member is expelled between the terminal connection adjacent and the conductor connected to said sealing member.

3. A fuse including a fuse tube, terminal connections therefor, a conductor connecting to said terminal connections, at least a portion thereof being readily fusible, a sealing member electrically connecting said conductor to one of said terminal members adapted normally to close one end of said fuse tube, an insulating tubular thrust member within said tube containing part of said terminal connections and extending toward said sealing member, said thrust member being adapted to be expelled by the gases formed by the blowing of the fusible member, and thereby to create an insulating path when said sealing member is expelled, between the conductor adjacent to said sealing member and its adjacent terminal connection, insulating material between said thrust member and said tube, said insulating material being adapted to be injected into the are formed between said sealing member terminal and the conductor adjacent to said sealing member when said sealing member is opened.

4. A fuse including a fuse tube, terminal connections therefor, a conductor connecting said terminal connections, at least a portion thereof being readily fusible, a sealing member adapted normally to close one end of said fuse tube, an insulating tubular thrust member within said tube containing part of said terminal connections and extending toward said sealing member, said thrust member being adapted to be expelled by the gases formed by the blowing of the fusible member, and thereby to create an insulating path when said sealing member is expelled, between the adjacent terminal connection and the conductor adjacent to said sealing member, and insulating material between said thrust member and said tube, said insulating material being adapted to be injected into the are formed between said terminal and said conductor adjacent to said sealing member when said sealing member is opened, and an insulating guide from the terminal connection adjacent to said sealing terminal adapted to restrict and direct the flow of insulating material between said thrust member and the last mentioned terminal connection.

5. A fuse including a fuse tube, terminal connections therefor, a conductor within said fuse tube establishing an electrical circuit between said terminal connections, at least a portion thereof being readily fusible, a sealing member serving to complete such electrical circuit between said conductor and one of said terminal connections and adapted normally to close one end of said fuse tube, a thrust member movable within said tube and forming therewith a closed compartment for such readily fusible portion of said conductor said thrust member extending therefrom toward said sealing member and adapted to transmit the force caused by the expanding gases resulting from the blowing of the fuse directly to the sealing member, to expel the same whereby the tube is rapidly unsealed and a secondary break in such electrical circuit is rapidly effected at the annular opening created by such expulsion at the end of the fuse tube whereby such break is directly in the path of the expelled gas.

6. A fuse including a fuse tube, terminal connections therefor, a conductor within said fuse tube establishing an electrical circuit between said connections at least a portion thereof being readily fusible, a sealing member adapted normally to close one end of said fuse tube, a thrust member movable within said fuse tube and forming therewith a closed compartment for such readily fusible portion of said conductor said thrust member comprising a tube of insulating material normally closed at one end by said sealing member, thus providing within said thrust member an air reservoir adapted to cushion sudden pressures caused by blowing of the fuse by compression of the air therein and transmitting such pressure to the sealing member to unseal the fuse tube by a combination of pressure through the air column and through the annular wall of the thrust member.

7. A fuse as described in claim 6 and including a sealing member for the opposite end of said thrust member adapted to be displaced by excessive pressures within said fuse tube permitting the cushioning of the pressure through the air column contained therein but serving as a closure under less violent fusion of said fuse.

8. A fuse including a fuse tube, terminal connections therefor, a conductor within said fuse tube establishing an electrical circuit between said terminal connections, at least a portion thereof being readily fusible, a sealing member normally closing one endof said fuse tube, a thrust member movable within said fuse tube and forming therewith a closed compartment for the readily fusible portion of said conductor and adapted to directly transmit pressure between said closed compartment and said sealing member, said thrust member comprising a tube of insulating material surrounding a portion of said conductor.

9. A fuse including a fuse tube, terminal connections therefor, a conductor within said fuse tube establishing an electrical circuit between said terminal connections, at least a portion thereof being readily fusible, a sealing member normally closing one end of said fuse tube, a thrust member movable within said fuse tube and forming therewith a closed compartment for the readily fusible portion of said conductor, said thrust member being rigid but of relatively small section permitting its collapse under excessive pressure.

10. A fuse including a fuse tube, terminal connections therefor, a conductor within said fuse tube establishing an electrical circuit between said terminal connections, at least a portion thereof being readily fusible, a sealing member normally closing one end of said fuse tube, a tubular thrust member of light weight movable within said fuse tube and forming therewith a closed compartment for the readily fusible por tion of said conductor, said sealing member also being of relatively small mass whereby rapid ac tion to unseal the fuse tube is secured.

11. A fuse including a fuse tube, terminal connections therefor, a conductor within said fuse tube establishing an electrical circuit between said terminal connections, at least a portion thereof being readily fusible, a metallic sealing member forming a part of such electrical circuit and normally closing one end of said fuse tube, a thrust member of insulating material movable within said fuse tube and forming therewith a closed compartment for the readily fusible por tion whereby unsealing of the fuse tube by action of said thrust member will serve to effect an additional break in the electrical circuit.

12. A fuse as described in claim 8 in which said thrust member and the portion of said conductor surrounded thereby cooperate to move the portion of said conductor adjacent said easily fusible portion away from the closed compartment at a speed greater than that of said thrust member.

13. A fuse as described in claim 8 in which said conductor passes around the end of said thrust member adjacent the associated sealing member and is attached to the adjacent terminal.

14. A fuse as described in claim in which said thrust member is of insulating material.

15. A fuse including a fuse tube, terminal connections therefor, a conductor within said fuse tube establishing an electrical circuit between said terminal connections, at least a portion thereof being readily fusible, a sealing member normally closing one end of said fuse tube, and forming a link in such electrical circuit, are extinguishing material retained by said sealing member, a tubular member extending through said are extinguishing material and adapted to conduct gas pressure resulting from fusing of said fusible portion to said sealing member to expel the same to effect a secondary break in such electrical circuit and to release such are extinguishing material adjacent such secondary break.

16. A fuse as described in claim 15 in which said tubular member is movable by said gas pressure through said are extinguishing material to agitate the same.

17. A fuse as described in claim 15 in which said tubular member also separates said fusible portion from said are extinguishing material prior to expulsion of said sealing member and is movable to permit passage of gas to act upon said are extinguishing material subsequent to such expulsion.

18. A fuse as described in claim 15in which said tubular member is of insulating material and surrounds the portion of said conductor between said fusible portion and said sealing member.

19. A fuse including a fuse tube, terminal connections therefor, a conductor within said fuse tube establishing an electrical circuit between said terminal connections, at least a portion thereof being readily fusible, expellable sealing members normally closing both ends of said fuse tube, a tubular member forming a compartment for the readily fusible portion of said conductor, extending to one of said sealing members, and adapted to transmit gas pressure therethrough between said fusible portion and said sealing member and are extinguishing material retained by said sealing members, surrounding said tubular member, and between said fusible portion and said other sealing member adapted for expulsion from the fuse tube upon blowing of the fuse.

20. A fuse including a fuse tube, terminal connections therefor, a conductor within said fuse tube establishing an electrical circuit between said terminal connections, at least a portion thereof being readily fusible, expellable sealing members normally closing both ends of said fuse tube, a thrust member movable within said fuse tube and forming therewith a closed compartment for the readily fusible portion of said conductor said thrust member extending from such closed compartment to one of said sealing memhere, said fuse including a second thrust member extending from said closed compartment to the other sealing member.

21. A fuse including a fuse tube, terminal connections therefor, a conductor within said fuse tube establishing an electrical circuit between said terminal connections at least a portion thereof being readily fusible, a sealing member serving to complete such electrical circuit and adapted normally to close one end of said fuse tube, a thrust member movable within said fuse tube and forming therewith a closed compartment for such readily fusible portion of said conductor and adapted to transmit directly pressure caused by fusing of such readily fusible portion between said compartment and said sealing member, said fuse tube and said thrust member forming a second annular compartment surrounding said thrust member, and are extinguishing material within such annular space, said fuse including a guide of insulating material extending beyond said sealing member and the adjacent terminal connection adapted to restrict and direct the flow of arc extinguishing material between said terminal and said sealing member during expulsion of said are extinguishing material.

AUGUSTUS JESSE BOWIE. 

